ILLUSTRATIONS (23). ACICTJLAR-LEAVED TREES. 315 



Jura limestone. The vegetation of the eocene world presents 

 especially to us forms which, by their coeval relationship with 

 several families of the present world, remind us that with it 

 many intervening members have disappeared. The Coniferse, 

 so frequent in the primeval world, accompany, in particular, 

 the ligneous remains of Palms and Cycadese ; but in the most 

 recent beds of lignite or brown coal we again find Coniferse, 

 our Pines and Firs, associated with Cupuliferse (or Mastworts), 

 Maples and Poplars.* 



If the surface of the earth did not rise to great altitudes 

 within the tropics, the strikingly characteristic form of acicu- 

 lar-leaved trees would have remained wholly unknown to the 

 inhabitants of that zone. I took great pains, in common 

 with Bonpland, to trace out, in the Mexican Highlands, the 

 lower and upper boundary line of the Coniferse and Oaks. 

 The heights, at which both begin to grow (los Pinales y 

 Encinales, Pineta et Querceta), are hailed with joy by those 

 who come from the sea coast, because they announce a cli- 

 mate not yet invaded, as far as experience has hitherto shown, 

 by that mortal disease called the black vomit (vomito prieto, 

 a form of the yellow fever). For the oaks, especially the 

 Quercus Xalapensis (one of the twenty-two Mexican species of 

 oak which we first described), the lower line of vegetation, 

 on the way from Vera Cruz to the capital of Mexico, somewhat 

 below the Venta del Encero, is 3048 feet above the sea. At 

 the western slope of the plateau, between the South Sea and 

 Mexico, the inferior line for oaks is something lower ; it begins 

 near a hut named Venta de la Moxonera, between Acapulco 

 and Chilpanzingo, at the absolute height of 2481 feet. I 

 found a similar difference in the lower boundary line of the 

 pine-forest. This boundary, towards the South Sea, in the 

 Alto de los Caxones, north of Quaxinquilapa, is for the Pinus 

 Montezumse (Lamb.), which we at first had considered to be 

 the Pinus occidentalis (Swartz), at the height of 4092 feet; 

 but towards Vera Cruz, at the Cuesta del Soldado, it rises to 

 5979 feet. Both these kinds of tree, therefore, the oaks and 

 firs as specified above, descended lower towards the Pacific 

 than towards the Caribbean Gulf. During my ascent of the 

 Cofre di Perote, I found the superior boundary Hne of the oaka 

 to be 10,353 feet; that of the Pinus Montezumae 12,936 feet 

 (about 2000 feet higher than the summit of Mount ^Etna) 

 * See Cosmos, vol. i. pp. 282-287 (Bohn'3 edition). 



